Blade construction for turbines



July 23, 1968 E. P. NISKANEN 3,393,893

BLADE CONSTRUCTION FOR TURBIINES Filed Feb. 7, 1966 2 Sheets-Sheet 1 l'5m l f/// ll FIG. 1

July 23, 1968 E, P, NNNNNN EN 3,393,893

\ A Nw v wy S' United States 4Patent O 3,393,893 BLADE CONSTRUCTION FORTURBINES Erkki Pietari Niskanen, Kissankellontie 13, Helsinki, FinlandFiled Feb. 7, 1966, Ser. No. 525,582 Claims priority, applicationSweden, Feb. 9, 1965,

,654/65 3 Claims. (Cl. 253-165) ABSTRACT OF THE DISCLOSURE A bladeconstruction for a turbine wherein annular arrays of blades on a rotorwheel, which are directed inwardly towards the axis of rotation of thewheel, are each secured at their inner ends to a common ring which isreceived in a groove of another wheel having radially outwards arrays of-blades which are interdigitated with the blades of the first wheel, theouter ends of the inwardly directed blades being slidably received inthe associated wheel for radial movement.

The present invention relates to a blade construction for turbinesespecially for axial iiow turbines with rotor wheels rotating inopposite directions and provided with rings of blade.

In steam and gas turbines of this kind, in which two turbine rotorsrotate inside one another forming axial iiow channels lfor the power andare provided with rings of blade which protrude into these flow channelsand are alternatively directed inwards and outwards, the blades of suchinwardly directed rings become subject to a certain bucking action dueto the centrifugal force of the rotating rotor wheels, because theinwardly directed blades in question are supported mainly at theirradially outer ends by the respective rotor wheels. It is known tosupport the blades of such inwardly directed -blade rings at theirradially inner ends by means of relatively thin shroud rings, which,however, cannot receive the strains acting on the blades. Thus thebuckling action mentioned above irnposes certain restrictions on theblades as far as suitable shape, dimensions and working conditions areconcerned.

The object of the present invention is to eliminate this disadvantageand the arrangement according to the invention is mainly characterizedby the fact that the blades in each blade ring, which extends towardsthe axis of rotation, are radially slidably joined at their outer endswith the rotor wheel body supporting said blade ring, and

radially tixedly joined at their inner ends with a support ring, whichis common for all blades of said blade ring and is dimensioned so thatthe entire radial strain, to which the blades are subject due tocentrifugal force, is received at the inner ends of the blades by meansof the support ring.

By supporting those blades, which are directed inwardly towards the axisof rotation, at their radially inner ends, it is achieved that thestrain, to which the blades are subject because of the centrifugalforce, is received entirely at the inner ends of the blades by means ofthe support ring, thus effectively eliminating the buckling strainacting on the blades. The torque produced in the blades by the powermedium is transmitted in the usual way by the blades to the rtoor wheelbody, to which the blades are attached radially slidably at theiropposite outer ends in relation to the support ring.

Owing to the support ring according to the present invention, the rotorwheel body will, to some extent, be relieved of strains and its rnasscan be reduced in view of the strain, which now according to theinvention is received by the support ring. In this case the mass of thesupport ring can, however, be made less than the mass by lCC which theblade wheel body can be reduced by means of the support ring, becausethe support ring is at a lesser radial distance from the axis ofrotation than the rotor wheel body, and the support ring is consequentlysubject to less centrifugal strain. By the blade construction accordingto the invention there is thus achieved not only an elimination of theblade buckling risk, but also the considerable advantage that the totalmass of the rotor wheel bodies and the support rings is less than themass of the rotor wheel bodies in conventional turbines, while inaddition the diameter of the turbines can -be reduced.

When applying the present invention to a turbine, where the rotor wheelbodies are composed of a number of ring shaped sections, which arejoined axially one behind the other and which support the respectiveblade rings, it is suitable to provide for each supporting ring acircumferential groove in the interplane between two rotor wheel bodysections, which groove encloses the respective support ring with acertain clearance. The mounting of the rotor wheel bodies can now beeffected by arranging the various sections of the two rotor wheel bodiesone by one axially behind each other and by joining adjacent sectionsbelonging to the same rotor wheel body with each other.

A more detailed description of the invention is given below withreference to the attached drawing, where FIG. 1 is an axial crosssectional view of one embodiment of a turbine provided with a bladeconstruction according to the invention,

FIG. 2 is a cross sectional view taken along line II-II in FIG. 1 andFIG. 3 is a cross sectional view of a support ring according to anotherembodiment of the invention.

In the drawing only an outline of the turbine construction has beengiven, and turbine parts which are unimportant for an understanding ofthe invention have been left out.

The turbine comprises two co-axially arranged shafts 1 and 2, whichrotate in opposite directions and each support a rotor wheel 3 and 4,which are arranged with their blade supporting bodies 31, 41 and 42interengaged to form axial ring shaped flow passages 5 and 6. The bodiesof the rotor wheels are provided with annular arrays or rings of bladeswhich alternately protrude into said passages from both rotor wheels ininterdigitating fashion. The body 31 of one rotor wheel 3 is fitted witha ring of blades 32, in which the blades extend radially inwardly towardthe axis of rotation, and a ring of blades 33, in which the bladesextend radially outwardly. The body of the other rotor wheel is fittedwith a ring of blades 43, in which the -blades extending radiallyoutwardly and the body part 42 is fitted with a ring of blades 44, inwhich the blades extend radially inwardly. A steam inlet is designatedby reference numeral 7 and steam passes from the inlet 7 throughopenings 8 in the rotor wheel 3 into a common inner space 9 of the rotorwheels and further on through channels 10 in the rotor wheel 3, the flowpassage 5, reversing channels 11 in the rotor wheel 4 and finallythrough the ow passage 6.

In accordance with the present invention, the blades of each blade ring,which extend radially inwardly towards the axis of rotation, areradially xedly joined at their inner ends with a support yring and attheir outer ends are radially slidalbly joined with the rotor wheel bodysupporting said blades. Therefore, the blades of the blade ring 32 are,as shown in FIG. 2, provided at their inner ends with fastening means36, which are radially Iixedly mounted in a support ring 34, and attheir outer ends with fastening means 37, which are radially slida-blymounted in the body 31 of the rotor wheel 3. The rblade-s of the bladering 44 are similarly joined with the support 3 rings 45 and the -body42. The support rings are co-axial with the turbine shafts 1 and 2 `anddimensioned so that the entire radial strain, to which the blades 32, 44are subject due to the centrifugal force produced by the rotation of therotor wheel, is resisted by the support rings 34 and 45, respectively,so that the blades 32, 44 do not exert any radial forces, but onlyperipheral torque on the bodies 31 and 42 respectively. In the innerbody 41 of the rotor wheel 4, peripheral grooves 46 have been providedexactly in line with the support rings 34, and in the body 31 of theother rotor wheel, peripheral grooves 35 have been provided for thesupport rings 45, which grooves with a certain clearance enclose therespective support rings in such a manner that the support rings do notobstruct the axially evenly diverging shape of the flow passages 5 and 6in the direction of the ow.

As appears from FIG. 1, the bodies 31, 41 and 42 of the rotor wheelbodies are composed of separate rings shaped sections 31', 41 and 42,the interplane of they sections being substantially parallel to eachother and perpendicular to the axes of rotation of the turbines. In eachcase the peripheral grooves 35, 46 have been arranged exactly in linewith the interface between two blade wheel sections so that the twosections together limit the peripheral groove. When using a sectionalconstruction of this kind, the mounting of the rotor wheels can beeffected by arranging the various sections of the rotor wheel bodies oneby one alternately and axially behind each other and by joining adjacentsections belonging to one and the same rotor wheel body with each otherand With the respective rotor wheel.

A turbine which has been provided with a blade construction according tothe invention, operates in a manner, which is in itself previouslyknown, but at the same time it has the advantages indicated in thepreamble of the specification, as compared with conventional bladeconstructions.

The drawing and the corresponding part of the specication are onlyintended to illustrate the idea of the invention. The details of theblade construction according to the invention may vary considerablywithin the scope of the patent claims. Thus the support rings can beshaped in various ways, as has been shown by way of example in FIG. 3.

What I claim is:

1. A turbine comprising a pair of shafts arranged coaxially for rotationin opposite directions about a common axis, a rotor wheel on each shaftrotatable therewith, said wheels including respective axially spacedarrays of blades arranged around said axis of rotation, the blades onone lwheel extending radially inwards towards said axis and the bladesof the other wheel extending radially outwards away from said axis, theblades of said wheels alternating axially and being interdigitated, asupport ring for each of the arrays of blades which extends radiallyinwards, each said support ring being mounted coaxially with said shaftsand being connected to the inner ends of all of the blades of theassociated array in radially iixed relation, the outer ends of thelatter array of blades being slidably mounted for radial movement in theassociated wheel, each support ring being dimensioned so that the entireradial force applied to the blades by centrifugal force is resisted :bythe ring at the inner ends of the blades.

2. A turbine as claimed in claim 1, wherein each wheel has arrays ofblades which respectively extend radially inwards and outwards.

3. A turbine as claimed in claim 1, wherein each rotor wheel comprises aplurality of annular sections joined together in axial relation andsupporting Irespective arrays of blades, the annular sections whichcarry the radially outwardly extending blades having annular peripheralgrooves -between adjacent arrays of blades, which grooves are alignedwith the arrays of blades extending `radially inwards, said supportrings being accommodated in said grooves with slight clearance.

References Cited UNITED STATES PATENTS 824,449 6/1906 Stuart 253--71 X2,530,908 11/1950 Ray. 2,838,275 6/1958 Harris et al.

FOREIGN PATENTS 564,639 6/1957 Italy.

EVERETTE A. POWELL, JR., Primary Examiner.

